Telephone system.



W. AITKEN.

TELEPHONE SYSTEM.

APPLICATION FILED FEB. 25, I916.

3 SHEETS-SHEET 1.

w. AITKENE TELEPHONE SYSTEM.

APPLICATION FILED FEB. 25. 1916.

3 SHEETSSHEET 2- ZVG/ 1V6? //a/ 420/ 20/40 150/ k/a/wzaama 252/ W. AITKEN.

TELEPHONE SYSTEM.

APPLICATION FILED FEB. 25, 19:6.

Patented Ap 1'7, 3 SHEETSSHET 3.

five)? Z1071;

WILLIAM AITKEN, LONDON, ENGLAND ASSIGNOR TO RELAY AUTOMATIQ TELEPHONE COMPANY, LIMITED, OF LONDON, ENGLAND;

TELEPHONE SYSTEM.

nections. Owing to the relatively small capacity of the switches used in automatic telephone systems, the. subscribers lines and the junction lines are divided into small groups having access to a particular group only of all the outgoing junctions of I the corresponding switching stage. It is known that this 7 grouping of the lines increases the total number of junctions required, and consequently reduces the traffic carrying efficiency of the junctions due to the greater traffic variations in small groups. It is also recognized that the larger the groups of junctions Worked in,

common, the more efficient is the service and the fewer the total number of junctions required to carry the traffic. The maximum number of-junctions of each group is, however, as stated above, chiefly determined by the capacityof the switches.

It has been pro-posed to improve the efficiency of the junctions by interconnecting an additional switching stage, thereby giving the incoming lines access to a larger number of outgoing lines without increasing the capacity of the switches. The known double pie-selecting system is an example of this method of increasing the efficiency of the junctions without increasing the capacity of the switches.

According to another system the same object is attained without the use of additional switches merely by dividing the multiple ofthe switches in a suitable manner as-described in British Patents No. 22715 of 1914: and No. 20453 of 191.4. The arrangement is principally as follows j A group of outgoing lines of a switching stage is arranged in a number of sub-groups, each accessible to a particular group of incoming lines and adapted to carry only Specification of Letters Patent.

Patented A t. 1'7, 1917.

Application filed February 25, 1916. Serial No. 80,456

about the normal outward traffic of the associated group, and 1n 7 one or more other groups accessible in common to all or a large part of the incoming lines, and adapted to carry the peak loads of all associated groups of 1ncoming lines, the relative number of lines of the various groups being such that the traffic carrying capacity and efficiency of the total of said groups of outgoing lines become practically equal to that of an undivided group serving an equal number of ncoming lines. The first mentioned outgoing lines may be called first choice lines and the latter second choice lines, and the arrangement is such that no second choice line is taken into use until the first choice lines of a sub-group are all engaged.

The present invention relates to systems of the kind last mentioned and has for its object further to increase the efficiency of such systems as Will be hereinafter described with reference to the accompanying drawings.

Every means for increasing the efiiciency of the junctions without increasing the capacity of the switches is evidently also a means for reducing the capacity of the switches without affecting the efficiency of the junctions. This fact is of special importance to automatic systems in which the connections are built up by means of relays only, and in which the switches consequently consist of relays, the economy of such systems being in a higher degree than in other systems dependent on the capacity of the switches. In the following the invention will be described as having for its main object :to reduce the capacity of the switches, although of course it may be used for any of the said purposes and in any automatic system. The invention can be applied to the pre-selecting as well as to the group-selecting stages, and is not limited to the use of switches of any particular type.

In the accompanying drawings Figure 1 is a diagram illustrating the I principal features of the present invention,

Fig. 2 shows the invention as applied to the second pie-selecting stage of a system having primary and secondary pie-selectors,

Fig. 3 shows the inventionv as applied to group selecting stages, and i Fig. 4 the actual circuits of the switches of a group-selecting stage.

According to the present invention each group G of incoming lines is divided into no sub-groups g as shown in 1, and the first choice groups of outgoing lines are correspondingly divided into first and second calling line are all engaged, and no third.

choice line is taken into use until all corresponding first and second choice lines are engaged.

The grouping should be so carried out that all first and second choice lines may it possible be engaged during the busiest hour of the day.

The effect of thus grouping the junctions into first, second and third choice linesis, as can be readily understood, a reduction of the capacity of the-switches without affecting the efficiency of the junctions as to their ability to carry the traffic.

The essential feature of the invention will be evident from the following If the first and second choice line arrangement is considered as a principal or primary grouping or line scheme, the grouping scheme according to Fig. 1 may be regarded as composed of two primary line schemes united by the third choice lines to a secondary scheme which in its main structure is similar to a primary scheme, but is of a higher order inasmuch as it comprises first, second and third choice line groups. In a similar manner secondary line schemes may be used to form tertiary schemes and so on, whereby the junctions may be divided into first, second, third and fourth choice groups,

or any wanted number of groups available in succession. The number of incoming line groups of a primary scheme as well as the number of schemes contained in a scheme of a higher order are of course immaterial to the'invention, and may be any number consistent with the traffic requirements. For instance, each primary scheme of Fig. 1 may contain three or more groups 9 by which the second choice group 20 is used in common, and there may be three or more such primary schemes to which the third choice group 30 is common.

In accordance with the sub-division of the outgoing lines, the incoming lines are divided into primary, secondary, tertiary groups, etc., the primary groups 9' being the incoming line groups of a primary scheme, the secondary groups G the incoming line groups of a secondary scheme, and so on.

Fig. 2 shows one form of the invention as applied to the second pre-selecting stage of an automatic telephone system, having primary and secondary pro-selectors. As stated above, the invention chiefly consists only in a particular method of dividing the multiple of the switches whereby the ciiiciency of the masses junctions may be increased without the use of additional switches in accordance with the known double selecting method, but it is apparent that an increased efiect is attained by using both methods in combination, as shown in Fig. 2.

The figure represents a line arrangement for 1000 subscribers lines S having access through intermediate lines I to 50 junctions J leading to first selectors. The subscribers lines aredivided into hundred and fifty line groups, S1, S2, S3, etc., and s1, s2 respectively. Each hundred line group S has access to a group 2' of 10 intermediate unctions l which are divided into 2 first choice groups '11C1 and 11C2, including three lines each,

and one second choice group 12C comprising four lines, each first choice group being accessible only to 50 subscribers, while the second choice group is accessible to all sub scribers of the hundred line group.

The 50 junctions J are divided into 10 first choice groups 21Cl, 21(12, etc., comprising thrce lines each, two second choice groups 2201 and 22(2 comprising seven lines each, and one third choice group 280 consisting of six, lines. Each first choice group 21C is accessible only to a particular primary group i of intermediate junctions, while each second choice group 226 is accessible to a secondary group T1 or 12 comprising five primary groups 2'. The third choice group 23C is accessible to all intermediate junctions. The number of lines of the various first, second and third choice I groups of the second stage is to be adapted Fig. 3 shows principally the line arrangement in a group selecting or digit stage.

A group of incoming junctions is divided into 12 sub-groups 7' each having access to two first choice lines 11C and 21C of each numerical group of outgoing lines. drawing, only two such numerical groups NGl and NGEZ are shown- Further, two second choice lines, 12C and 226, are ar ranged in common to every group of two sub-groups 7', three third choice lines 13C and 23C, in common to every group of tour In the i sub-groups j, three fourth choice line 14C and 24C in common to every group of six sub-groups j and three fifth choice lines 150 and 25C in common to all sub-groups j. i

The switches may be associated with the incoming junctions, in which case the outgoing lines are connected to the multiple of said switches according to the described division oi the same into first, second third,

fourth and fifth choice groups. The operation of the switches is so controlled that a second choice line is not taken into use until the appertaining first choice lines are all engaged, and a third choice line is not taken into use until all first and second choice lines are engaged, and so on.

outgoing-junctions, while the selector S'Z,

completes the connection with an idle junction of said group. In the diagram, only two outgoing junctions J1 and J X, belonging to'the first numerical group, are shown, whereas the third or test wires TW of all junctions of said first numerical group are represented, and it is to be understood that the line wires LWl a'nd LWQ are multiplied over the relays of the selector Si in a manner similar to that "in which the test wires TW are multiplied. In this case it may be assumed that the outgoing junctions are divided into first, second and third choice groups'llCl, 1201 and 13C1. J1 is then the first of the first choice junctions, and J X is v the last of the third choice junctions.

A subscriber having been connected to the junction P completes a circuit 1 through his circuits 2a,'2b and 3 are completed, the first being a locking circuit for L, the second an operating circuit for H through a'contact of L and the third operating retarded release relay RR2 to prevent closing of circuits 5 and-11. As soon as H operates, it completes circuit 4 to energize relay M. At the termination of'the first impulse, LR is again ener gized and is maintained energized (as in this case only one numerical impulse is being sent),to allow relay RR2 to be deenergized. LR also breaks circuits 2a and Qb-a'nd con1 pletes circuit 2c, the latter to hold H energized. Due to the breaking of the circuit 2a, L deenergizes, completing circuit 5 through contacts of relays RR2, M and Crl and through the coil of relay S, and also completing circuit 6 through cut-off relay CO, which cuts out the line relay and extends the junction P as far as to the open contacts on CR1, H being also energized. S operating completes circuit 7 through control relay C and connects the code wires Cl" to the coils T, ll. V, \V, X of the idle line selector Si.

numerical group to theirrespective coils AR C operating completes circuit 8 through relay E to connect earth to the coding springs 9 and also connects the third or test wires T'lV of all the junctions ofthe selected first of the assignor A. .If all the junctions are, free, none of the assignor relays AR will be energized, consequently circuit 9 will be completed from earth over the back contact of assignor relay AR1,- code wire 9, and thence through relay X of 'selector- Si. X will energize, and with the energization of CR1 will connect P to J 1. CR1 is at the same time energized through the springs of selector Si to the third wire of junction J1 (circuit 10). CR1 operating completes circuit 11 to hold X energized and breaking circuit 5 releases S which denergizingdisconnects the code wires from Si and also releases assignor A by breaking circuit '7.

The contacts of the relays AR are so connected that the selector Si is always operated to establish connection with the first idle junction counting from junction J1 to J X. As a consequence the assignor automatically operates according to the invention to fill up all precedinggroups before a junction of the subsequent group is taken into use. The invention therefore does not in any way affect the construction of the switches and the circuits. Its main feature, as already stated above, is to be seen in-the particular division of the multiple of the switches. 1 If, forinstance, there is only one junction free, and that is junction J X, all the coding relays AR would be energized except AR5 associated with junction J X. Circuit 15 will therefore connect earth over front contacts of ARl to AR4 and back contacts of AR5 to the coding wires and to all the relays T, U, V, W, X of the selector Si. This will result in P being connected over front contacts of all the relays of Si to J X.

If the call had been to a subscriber in the second numerical group, L would be connected by St to' PZ. This would be effected as follows The loop of P- due to a subscriber being connected thereto would operate LR and earthon the thi d wire would energize RRl. The energization of these two relays would complete circuit 2 to operate L of selector St. At the first impulse; LR would le energize, completing circuit 3 through RR),

and circuits 2a and 2?), the former being a 1 local circuit to L and the latter operating H. On the loop being again closed, L would be released and circuits 2c and 4 would be formed, 20 being a locking circuit for H and 4 an operating circuit for M. .On loop lock M and the second to energize I. On I energizing, circuit 14' would be formed to energize N over a front contact of I and back contact of J. When LR again enerto P2 and due to the energization of L, M,.

N, a circuit 18a would be completed to a relay corresponding to S and associated with another selector of idle lines in the second 1000 line section. Circuit 18 would be formed to operate CO.

It will be seen that during the whole period of a conversation the impulse responder St and the selector Si must be held operated and must .be under the control of the calling subscriber connected with P.

St is retained energized so long as an earth is maintained on the wire EW due to the energization of RRl. This isheld energized so long as a subscriber is connected to P by earth on wire 1a. Si is held energized by a circuit (11) over contacts on St and a contact on CR1. As soon therefore as the subscriber initiating the call releases P, the impulse responder is free, the relays of which, denergizing, break holding circuit 11 of S2, which in its turn releases, disconnecting P from J to which it had been connected. i

The invention is'applicable to any electromechanical system. Thus, in a system using wipers passing over banks of 10 contacts,

the first five contacts may be first choice lines and contacts 6 to 10 second choice lines, or if larger groups are required, one level may be utilized for the first choice lines, and the second level for second choice lines, the shaft being stepped up automatically in a known manner to the second choice lines, it all the first choice lines are engaged.

in systems having movement in one direction only, the first 10 contacts may be first choice lines and the second 10 second choice, or the contacts may be otherwise suitably divided.

What I claim is 1. In a telephone system, the combination of a number of groups of incoming lines, each group being divided into a number of subgroups, a group of first choice outgoing lines associated with each sub-group of incoming lines, means for connecting an in: coming line to a first choice line, a number of groups of second choice outgoing lines,

maaoao when all the first choice lines available to an incoming line are busy, to connect an incoming line to a second choice line, a number of third choiceoutgoing lines available in common to a number of groups of incoming lines and means adapted, when all the first and second choice lines available to an incoming line are busy, to connect such incoming line to a third choice line.

2, In a telephone system, the combination of a number of groups of lines incoming to a switching unit, each group being divided into a number of sub-groups, a group of first choice lines connecting such unit to a second switching unit and associated with each sub-group of incoming lines, switches adapted to connect an incoming line to a first choice line, a number of groups of second choice lines connecting the first unit to the second switching unit, each of such groups being associated with a group of incoming lines, switches adapted, when all the first choice lilies available to an incoming line are busy, to connect an incoming line to a second choice line, anumber of third choice lines connecting the first unit to the second switching unit and available in common to a number of groups of incoming lines, switches adapted, when all the first and second choice lines available to an incoming line are busy, to connect such incoming line to a third choice line, such first, second and third choice lines being divided into a number of groups and each group being divided into a number of sub-groups, a group of first choice lines outgoing from the second switching unit, and associated with each sub-group of connecting lines, switches adapted to con; nect a connecting line to a first choice outgoing line, a number of groups of second choice outgoing lines, each of such groups being associated with a group of connecting lines, switches adapted, when all the first choice outgoing lines available to a connecting line are busy, to connect such connecting line to a second choice outgoing line, a 3 1111111" ber of third choice outgoing lines available in common to a number of groups oi con necting lines and switches adapted, when all the first and second choice out oing lines available to a connecting line are busy, to l connect such connecting line to third choice outgoing line,

AllTKEll-T. 

